Traditional wood-burning fireplaces are enjoyed for their attractive appearance, the "atmosphere" that their use creates, and their heat producing ability. However, there are many drawbacks to wood-burning fireplaces, among them the necessity for cleaning the chimney of soot to prevent chimney fires, and the build-up of wood ash in the hearth which must be periodically removed. In addition, wood for a fireplace is usually more expensive in urban settings than other fuels, such as gas, and it is difficult, or impossible, to install wood-burning fireplaces in many areas. Furthermore, wood is not completely combusted in most wood-burning fireplaces, and this produces ash and soot which enter the atmosphere and contribute to pollution.
On the other hand, gas-burning fireplaces can be installed in a wider variety of locations, burn more efficiently to produce a greater amount of heat, are easier to maintain, produce less pollutants, and are less expensive to utilize. However, the clean, hot flame produced by a gas burner does not have the same attractive appearance or provide the warm glow effect of the yellow/orange colored flame of a conventional wood-burning fireplace. Furthermore, the burner assembly of a gas-burning fireplace is not as attractive as a pile of wood blazing in the hearth of a wood-burning fireplace.
In an effort to enable gas-burning fireplaces to have a closer resemblance to wood-burning fireplaces, Coats, in U.S. Pat. No. 3,747,585, disclosed a simulated, non-combustible log structure supported above the burner of a gas-burning fireplace. Flames are permitted to contact the underside of the artificial logs to provide for a more realistic simulation of a wood-burning fireplace. However, no provision was made to color or modify the gas flames to resemble those produced from burning wood.
British Pat. No. 12,742, awarded to Oelbermann in 1902, noted that it was already old to color flames using a great variety of substances; these include metal salts or ashes, such as compounds of lithium, strontium, barium, copper, thorium, cerium, etc. Oelbermann produced a colored flame by projecting a holder filled with flame-coloring substances into a candle flame. However, this required an elaborate apparatus to maintain the holder in the candle flame since the candle would shrink in height as it was consumed.
Parker et al., in U.S. Pat. No. 4,472,135, improved upon the teachings of Oelbermann to produce a flame-coloring device for gas burners which makes the flame visible even when the burner is used outdoors or in a bright environment. A carrier is placed on the burner barrel, and a solid colorant emitter such as sodium chloride is supported by the carrier. However, the flame-coloring device has only been demonstrated to color flames of small conventional bunsentype burners. Furthermore, the colorant emitter used by Parker et al. is not heat-stable and may become molten at the temperatures employed to cause the colorant to drip off of the carrier, possibly clogging the burner and soiling the area surrounding the burner while also rapidly exhausting the flame colorant.
Salooja, in U.S. Pat. No. 3,925,001 recognized that heat-stable metal compounds could be used to catalytically improve the combustion of carbonatious fuels when applied to a support which is then placed in the center of the primary reaction zone of a flame. The catalytically active material is selected from compounds of barium and sodium, barium and yttrium, barium and erbium, aluminum, aluminum and yttrium, aluminum and lanthanum, aluminum and erbium, aluminum and platinum, gallium and sodium, zirconium and yttrium, zirconium and erbium, zirconium and chromium, zirconium and manganese, zirconium and iron, zirconium and platinum, manganese and sodium, manganese and yttrium, manganese and titanium, manganese and chromium, manganese and iron, manganese and nickel, and palladium and iron.
A critical aspect of Salooja's disclosure is the correct placement of the catalytically active material in the flame. Salooja recognized that all gas flames have a general structure comprised of three zones:
1. A cool zone at the base of the flame where air and fuel are mixed without substantial fuel combustion; PA1 2. A primary reaction zone, adjacent to the base of the flame; this -s the hottest part of the flame since combustion is most vigorous here and the concentration of ions is at a maximum; and PA1 3 Asecondary reaction zone, above and adjacent to the primary reaction zone; this is the most luminous part of a flame, and is usually substantially cooler than the primary reaction zone. If there is insufficient air, or if combustion is not complete, smoke and soot would appear above the secondary reaction zone. Only by placing Salooja's catalyst impregnated support in the primary reaction zone of a flame will there be a reduction in the production of soot and smoke and an increase in the efficiency of flame combustion. The catalyst impregnated support of Salooja will not work correctly if placed outside of the primary reaction zone, nor does it assist in coloring the flame.
Wood-burning flames generally burn cooler than gas flames and have larger secondary reaction zones due to the incomplete combustion of the wood components. However, gasburning fireplaces generally do not suffer from incomplete fuel combustion, nor do they generate significant quantities of smoke or soot. In fact, their high temperatures and efficient utilization of fuel causes the secondary reaction zone of a gas-burning fireplace flame to be almost invisible. For example, the primary reaction zone of a natural gas flame burning in air may achieve temperatures in excess of 3400.degree. F. (depending on the fuel to oxidant ratio) while the secondary reaction zone may have temperatures ranging down to approximately 1000.degree. F.
The high temperatures achieved in a gas-burning fireplace may pose potential fire and explosion hazards if the fireplace is not correctly designed and used. As a result, gas-burning fireplaces should meet appropriate safety standards such as those set by the American National Standards Institute, ANSI. Existing flame-coloring methods, if they were to be used in conjunction with an ANSI approved gas burner, may not be capable of certification under ANSI or other safety standards.
There is thus a need for a gas-burning fireplace in which fuel is burned efficiently and cleanly, but which also has a secondary reaction zone which has the color and appearance of a wood-burning flame. There is also a need for a device which can provide uniform flame coloration for extended periods of time, can be easily replaced, is safe to use, and which has a flame-coloring substance which will not, when exposed to a flame, rapidly decompose, or flake and/or drip off to clog the burner and/or soil the surrounding area. A fireplace using such a device would combine the economical and improved heating capabilities of a gas-burning fireplace with the aesthetic beauty associated with wood-burning fireplaces.